The invention relates to an apparatus for refilling compressed-gas bottles, having a threaded connection and valve, especially for small gas bottles of a capacity of less than 1000 ml, and a rated fill pressure up to about 34 bar, by means of a combustible unjacketed cartridge yielding oxygen in the burning state, and having a cartridge holder accommodating the cartridge, from whose inner chamber the oxygen can be transferred to the compressed-gas bottle.
Gas producers using a mixture of chemical compounds from which oxygen is released by an exothermic reaction have long been known. As a rule, the mixture is one of an alkali metal chlorate or perchlorate and an oxidizable substance which, while burning after an igniting process, provides just enough heat for the reaction to progress at an approximately uniform rate of migration in the cartridge, while excess oxygen is continuously released. The reaction mixture is formed into a solid, pressed body, namely the cartridge mentioned above. The temperature in the reaction zone is about 650.degree. C.
From U.S. Pat. No. 3,573,001 it is known to provide such reaction mixtures in the form of a solid body with an electrical igniter, and with an insulating envelope of a filter material, and to insert it into a take-apart container which is provided with an opening for the continuous delivery of oxygen. However, the known apparatus is not suitable for refilling compressed-gas bottles, since the pressure in the gas generator must always be higher than it is on the receiver side. On account of its closure alone, the known container would be incapable of withstanding such a pressure build-up. Furthermore, the pressure build-up within the porous thermal insulation would cause the loss of a considerable portion of the oxygen.
The same U.S. Pat. No. 3,573,001 also discloses a pressure container having a storage chamber and an internal cartridge holder in which a plurality of cartridges is disposed, each with its own electrical igniting mechanism. The individual cartridges are progressively ignited by a pressure measuring device as the pressure drops. To prevent the combustion from running out of control through all of the cartridges, each individual cartridge must be surrounded by an individual jacket of thermal insulating material. This known apparatus is also unsuitable for use as an apparatus for refilling compressed-gas bottles, because in the event of a pressure equilibrium, which is ultimately possible, a considerable amount of the oxygen would be left in the storage chamber. Furthermore, since the built-in igniting mechanism has to operate step-wise, this apparatus is exceedingly complex.
U.S. Pat. No. 3,737,287 discloses an oxygen producer having a take-apart container into which jacketed cartridges with a built-in percussion igniter can be inserted. This known apparatus also has a storage chamber, and additionally a cavity of considerable size exists within the cartridge jacket. The apparatus is, again, not designed or suitable for operation for the refilling of compressed-gas bottles, because at the pressure equilibrium that is to be achieved in the most favorable case, considerable amounts of oxygen would remain in the container, to escape when the container is reopened for the purpose of recharging with a fresh cartridge. Although the container is called a pressure container, the pressure involved is only relatively low, since the illustrated container closure is not capable of withstanding very high pressures. As a precautionary measure, therefore, the container is equipped with a pressure relief valve. The cartridges, which are provided with a percussion igniter as well as a metal jacket, are relatively expensive, so that the operation of the apparatus is correspondingly expensive. German publication OS No. 2,461,681 discloses a refilling apparatus of the kind described in the beginning, which is designed, it is true, for larger compressed-gas bottles. Here, again, the cartridge holder is disposed in the interior of the container, which is definitely a compressed-gas bottle, and is in the form of a tube open at one end, whose interior is in permanent communication with the compressed-gas bottle. The cartridge holder which is open at one end and surmounted by a pressure gauge is therefore, in the present case, the actual refilling apparatus. This cartridge holder is charged with jacket-less cartridges, while it is not of any great importance how big the space surrounding the cartridges is, since it is precisely this chamber that receives the entire amount of oxygen released. The known apparatus, however, is correspondingly bulky, and as a whole is not suitable for refilling smaller compressed-gas bottles.
With regard to a refilling operation, furthermore, the following is to be noted: Since the oxygen can always flow only in the direction of diminishing pressure, the gas exchange between the gas producer and the compressed-gas bottle comes to a stop no later than when pressure equilibrium is reached, unless the pressure in the refilling apparatus has to be higher on account of the presence of a non-return valve. As a consequence, the oxygen losses are proportional to the ratio between the volume in the refilling apparatus and the volume in the bottle that is to be filled. Even if the capacities in the refilling apparatus on the one hand and in the bottle being filled on the other were to be equal, half of the oxygen would remain at half pressure in the refilling apparatus, and would be lost when the latter is disconnected, or when it is reloaded with a gas-yielding cartridge. Also the compressed-gas bottle being refilled will contain only half of the maximum amount of oxygen achievable, on account of the halving of the pressure. If the free volume or storage volume of the gas producer were still greater, the situation would be worse.
The invention is addressed to the problem of providing a refilling apparatus of the kind described in the beginning, whereby compressed-gas bottles, especially standardized small gas bottles, can be refilled with high-purity oxygen to a very high pressure, inexpensively and with a minimum loss of oxygen.